amcharts XY Scatter

HTML

<script src="http://www.amcharts.com/lib/amcharts.js" type="text/javascript"></script>
<div id="chartdiv" style="width: 100%; height: 359px;"></div>

JavaScript

var chart;

var chartData = [
{
    ax: 1,
    ay: 0.5,
    bx: 1,
    by: 2.2},
{
    ax: 2,
    ay: 1.3,
    bx: 2,
    by: 4.9},
{
    ax: 3,
    ay: 2.3,
    bx: 3,
    by: 5.1},
{
    ax: 4,
    ay: 2.8,
    bx: 4,
    by: 5.3},
{
    ax: 5,
    ay: 3.5,
    bx: 5,
    by: 6.1},
{
    ax: 6,
    ay: 5.1,
    bx: 6,
    by: 8.3},
{
    ax: 7,
    ay: 6.7,
    bx: 7,
    by: 10.5},
{
    ax: 8,
    ay: 8.0,
    bx: 8,
    by: 12.3},
{
    ax: 9,
    ay: 8.9,
    bx: 9,
    by: 14.5},
{
    ax: 10,
    ay: 9.7,
    bx: 10,
    by: 15.0},
{
    ax: 11,
    ay: 10.4,
    bx: 11,
    by: 18.8},
{
    ax: 15,
    ay: 12.4,
    bx: 12,
    by: 14.8},
{
    ax: 12,
    ay: 11.7,
    bx: 12,
    by: 19.0},
{
    ax: 1,
    ay: 0.5,
    bx: 1,
    by: 2.2}];

AmCharts.ready(function() {
    // XY CHART
    chart = new AmCharts.AmXYChart();
    chart.pathToImages = "http://www.amcharts.com/lib/images/";
    chart.marginRight = 0;
    chart.marginTop = 0;    
    chart.autoMarginOffset = 0;
    chart.dataProvider = chartData;
    chart.startDuration = 1;

    // AXES
    // X
    var xAxis = new AmCharts.ValueAxis();
    xAxis.position = "bottom";
    xAxis.axisAlpha = 0;
    xAxis.autoGridCount = true;
    chart.addValueAxis(xAxis);

    // Y
    var yAxis = new AmCharts.ValueAxis();
    yAxis.position = "left";
    yAxis.axisAlpha = 0;
    yAxis.autoGridCount = true;
    chart.addValueAxis(yAxis);

    // GRAPHS
    // triangles up            
    var graph1 = new AmCharts.AmGraph();
    graph1.lineColor = "#FF6600";
    graph1.balloonText = "x:[[x]] y:[[y]]";
    graph1.xField = "ax";
    graph1.yField = "ay";
    graph1.lineAlpha = 0;
    graph1.bullet = "triangleUp";
    chart.addGraph(graph1);

    // triangles down 
    var graph2 = new AmCharts.AmGraph();
    graph2.lineColor = "#FCD202";
    graph2.balloonText = "x:[[x]] y:[[y]]";
    graph2.xField = "bx";
    graph2.yField = "by";
    graph2.lineAlpha = 0;
    graph2.bullet = "triangleDown";
   ...